William Bramley/The Gods of Eden/21/216/3

Metal coins became a popular tool of barter because they were durable and quantities could be controlled. They did create some problems, however. Realistically, people were only trading pieces of metal for other goods. This created a disproportionate emphasis on metals. The acquisition of coins and coin metals became an obsession to a great many people, and such obsessions tend to drain away energy better spent producing other valuable goods and services. The system also gave a disproportionate amount of power to those who possessed large quantities of coined metals, even though other commodities, such as food, are ultimately more valuable. The person with the coin metals could immediately acquire any good or service, but a farmer first had to go through the intermediate step of exchanging his product for a coin or coin metal before he could have the same spending flexibility.